I had a hard time trying to install my picoboot, but after a lot of deception, I think that my rasp pico is the problem. After few weeks of soldering/desoldering/resoldering, I decided to try flashing GP2040 ( https://github.com/FeralAI/GP2040 ) and the controller buttons just stopped responding after few minutes. Glad that you could install it for your friends. I just replaced a faulty capacitor on the disk board and my GC returned to read disks and I kept with the hacked memcard solution to load homebrews.
sorry you hd trouble! if you want to send pics i can try to help but if a hacked memcard works for you thats fine too. with the price of games these days it's hard not to hack your gc/wii lol